Hydroformylating olefinic compounds is a reaction of great industrial importance and the majority of processes employ homogeneous catalysts dissolved in an organic phase comprising the reagents, products and possibly an excess of ligand, and so problems arise when separating and recovering the catalyst, in particular when the catalyst is used in relatively large quantities, as is the case with cobalt-based catalysts.
One solution to the problem has been mentioned by Bartik et al.: Organometallics (1993) 12, 164–170, J Organometal Chem (1994), 480, 15–21, and by Beller et al.: J Molecular Catal A: Chemical (1999), 143, 31–39. It consists of carrying out hydroformylation in the presence of an aqueous solution containing a cobalt complex which is rendered water-soluble by the presence of a phosphine-sulfonate ligand such as the sodium salt of trisulfonated triphenylphosphine or a trisulfonated tris(alkylphenyl)phosphine. International patent application WO-A-97/00132 describes cobalt clusters substituted by trialkoxysilylmethyl groups which renders them water-soluble. In that manner, the organic phase containing the aldehydes is readily separated from the aqueous phase containing the catalyst.
Despite the major industrial importance of said techniques for hydroformylating olefinic compounds, said two-phase systems suffer from a lack of solubility of the olefins in water, which results in relatively low reaction rates and makes them inapplicable to long chain olefins.
Further, U.S. Pat. No. 3,565,823 describes a technique consisting of dispersing a transition metal compound in a tin or germanium salt of a quaternary ammonium or phosphonium compound, with formula (R1R2R3R4Z)YX3 in which R1, R2, R3 and R4 are hydrocarbyl groups containing up to 18 carbon atoms, Z is nitrogen or phosphorus, Y is tin or germanium and X is a halogen, either chlorine or bromine. U.S. Pat. No. 3,832,391 describes a process for carbonylating olefins using the same composition. Those compositions suffer from the disadvantage of having a relatively high melting point, for example over 90° C., which complicates manipulation of the solutions of catalyst and reaction products.
U.S. Pat. No. 5,874,638, commonly assigned, describes benefiting both from employing two phases while avoiding the drawbacks due to using water, and from the use of compounds with high melting points by dissolving certain catalytic compounds of transition metals from groups 8, 9 and 10, known to catalyse hydroformylation, in non-aqueous ionic liquids constituted by organic-inorganic salts that are liquid at ambient temperatures. However, when the catalyst comprises a salt or a cobalt complex, it is very difficult to prevent at least partial formation of dicobalt-octacarbonyl and/or cobalt-tetracarbonyl hydride under the hydroformylation reaction conditions. These two compounds are highly soluble in the organic reaction phase constituted by at least the olefinic reagent and the aldehydes produced, and so recycling the cobalt using the non-aqueous ionic liquid phase is only partial, causing loss of catalyst.